for example, is a 1&8 a true 1&8 or is it a 1.75 or a 1.785? what say you?
I have a question about twist rates!
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Mark,
If it is engraved 1:8 it will be exactly that.
The slightly faster twists help stabilize heavier bullets in bigger calibres like the Creedmore. You don't need it in Grendel however because the smaller case favors lighter bullets. There are also potential downsides to faster twists so it's not just faster is better.
If you want to check, put an oversized patch on your cleaning rod. Start it down the barrel and it rotates with the rifling (as it should). Note the distance it takes to do one full rotation and measure.Last edited by Klem; 11-02-2023, 05:34 AM.
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Not really related to the OP's question, but I remember reading somewhere that if you have a rifle with a short barrel you'd want the twist to be slightly faster than if it had a longer barrel, all other things, including ammo, being equal. Supposedly it relates to MV and spin rate. Bullet doesn't come out as fast, so a faster twist will increase its 'RPMs' so to speak and help with stability (to be on par how it'd be with a longer barrel).
Sounded good to me at the time. I have no idea if there's any truth to it. Or if it even matters all that much in the general scheme.Last edited by SDW; 11-02-2023, 04:25 PM.
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NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
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I will add that you don't want to overstabilize bullets by having too fast a twist - they resist pointing down to the target after apogee. This is more noticeable in long range shooting.
Here is Shilen Rifles advice on twist rate:6.5mm/.264
- 7" * for bullets heavier than 130 gr.
- 8" for bullets heavier than 130 gr.
- 8" * Ratchet rifled 4 groove
- 9" for bullets up to 130 gr.
Kreiger twist rates for 6.5 are 1:7, 1:7.5, 1:8, 1:8.5, 1:9.
1:8 is the standard as it sits in the middle of what works. Still, lighter 6.5 bullets are more suited to 1:8 and slower.
I had a 1:7.5 to shoot 140gn Noslers in 6.5x47. Turned out it was less accurate than the Kriegers. I suspect that was down to the quality of the Pac-Nor barrel and not the twist rate, but I'll never know for sure.
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Gonna say, a bore brush works fine also for doing the measurement, whatever is handy. It was interesting to do this on (in?) my 1894 Marlin 44mag one time. 20" barrel and the rod just made it about half way through one spin before the brush came out the muzzle. LOL The rifle's got a 1:38" twist for some reason. I don't know why Marlin made them that way. It shoots okay for the kind of rifle it is, but it's certainly no tack driver.
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Berger twist rate calculator is pretty good at determining what you will need. https://bergerbullets.com/twist-rate-calculator/
There is a list of the berger bullets to select from but know a few things about you bullet and input those then calculate.
Polymer tipped bullets do not count the tip in the length for calculation.
SDW the 1:38 should be fine for a 44mag with 180 or 200gr bullets,I have seen some shoot 240s ok but others not so much.
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Originally posted by Klem View PostI will add that you don't want to overstabilize bullets by having too fast a twist
I just received a 12" Faxon 6.5 Grendel barrel with 1:8 twist. I plan to shoot 100-120 grain projectiles. If I wanted to shoot heavier bullets I would look for a 1:7.5 or 1:7 twist barrel. I don't see a reason to do so, however. If I need heavier bullets I'll use 8.6 blackout.
KWFrom my cold dead endmill...
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Originally posted by Klem View PostMark,
If it is engraved 1:8 it will be exactly that.
The slightly faster twists help stabilize heavier bullets in bigger calibres like the Creedmore. You don't need it in Grendel however because the smaller case favors lighter bullets. There are also potential downsides to faster twists so it's not just faster is better.
If you want to check, put an oversized patch on your cleaning rod. Start it down the barrel and it rotates with the rifling (as it should). Note the distance it takes to do one full rotation and measure.4x P100
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Originally posted by Konocti's Wigwam View PostI don't think it matters too much, it's not like 1:5 used on 300 blackout, or 1:3 used on 8.6 blackout. The twist has more to do with the projectile you use.
I just received a 12" Faxon 6.5 Grendel barrel with 1:8 twist. I plan to shoot 100-120 grain projectiles. If I wanted to shoot heavier bullets I would look for a 1:7.5 or 1:7 twist barrel. I don't see a reason to do so, however. If I need heavier bullets I'll use 8.6 blackout.
KW
Never been happy shooting animals with heavy subsonics; it's like shooting them with an accurate handgun, they rarely die immediately (humanely).
Here's a neat summary on Accurate Shooter.
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Originally posted by lazyengineer View PostDoes that actually work? Not being sparky, just wondering if the experimental error of that is enough to tell 1:8 vs 1:8.2,since everyone always says there are manufacturing aspects and its super common for a twist rate to be slower than specified (which I have no idea why that would be true ...)
As for seeing the difference between 8 and 8.2 I don't know, but a jammed tight patch does not slip so I don't see why not.
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Originally posted by lazyengineer View PostDoes that actually work? Not being sparky, just wondering if the experimental error of that is enough to tell 1:8 vs 1:8.2,since everyone always says there are manufacturing aspects and its super common for a twist rate to be slower than specified (which I have no idea why that would be true ...)
You can see where it makes a full rotation, then mark that length on the rod. Once the rod is removed from the barrel, measure how far that point is that it took to make a full revolution, and there is your twist rate.NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
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Originally posted by kmon View PostSDW the 1:38 should be fine for a 44mag with 180 or 200gr bullets, I have seen some shoot 240s ok but others not so much.
Back to Grendels, BFT specs his SixFive barrels to use 1:7.5. At least the under-20" barrels.
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